Combat trim off in a P38 is a must, manually trim elevators to neutral and (as long as both engines available) leave rudder and aileron trim neutral.......
With combat trim off you will find the following good things:
Keeps you from stalling too early
-Delays (IMHO) compressing
-Plane seems a little more nimble in the vertical
-Downside: if u r busy in combat and cant trim manually, u may have to hold some stick pressure (back or forward) just to keep the aircraft level. This can make gunnery a little difficult, but with the nose mounted guns, thats no too much trouble.
By all means use the autotrim features: level, angle, speed when u have time. They will trim the aircraft for you pretty well.
Difference in G,J and L models.
G is as fast as J or L, but because it cant accelerate as well and takes almost thrice as long as the J/L to reach top speed it gives the mpression of being slower as most cons will get away. However the G can roll and turn like a spit. Its the most nimble of them all. Also IMHO in a dive it doesnt compress as quickly as a J/L.
J and L have little difference except for the hydraulic boost ailerons on the L. The J is lighter than L and seems to handle low speeds (below 200mph) better (IMHO) than the L. At speeds below 250mph it can roll pretty well too (though not like a 38G).
Above 250mph, the G and J start having trouble rolling, but the 38L can roll like a FW190.
All have the same guns, but L carries the most ordnance.
Love the 38s guns, 150 rds 20mm (more than spits) 500rds per gun 50cals (more than even a P47).
10rkts and 2000lbs give it quite a punch. Pity so many use it as a kamikazie Jabbo machine:(